1. Technical Field
The present invention relates to a technique of converting a color tone of an image.
2. Related Art
In recent years, many image display devices, such as CRT displays, liquid crystal displays, plasma displays, and projectors, have a plurality of output modes of an image that is displayed. Such modes include a dynamic mode in which brightness or saturation is emphasized, a cinema mode in which correction to a color tone suitable for watching a movie is made, and the like.
As a technique of performing color conversion according to an output mode, there is a technique of using a three-dimensional lookup table (hereinafter, referred to as “3D-LUT”) (refer to JP-B-58-16180). The relationship of correspondence between an input color and an output color is recorded in the 3D-LUT. An image display device stores the 3D-LUT in a memory and converts a color tone by referring to the stored 3D-LUT. The image display device can meet various kinds of modes by properly rewriting the 3D-LUT stored in the memory according to an output mode.
In the 3D-LUT, the data volume is increased if color conversion is performed with high precision. As a result, the size of a circuit for performing color conversion is increased. For this reason, the circuit for performing color conversion was redesigned, in many cases, for every model according to the purpose of use and price range of an image display device. However, as an integration degree of an LSI increases in recent years, it has become possible to share a color conversion circuit with relatively low cost even if a circuit is not designed for every model. However, among image display devices, there is an image display device, such as a low-cost projector used for presentation, which does not require such precision of color conversion. Accordingly, in the case of sharing a circuit on the basis of the specification of a high-class model, there was a case in which the excessive quality was obtained depending on a model of an image display device. In addition, if the data volume of the 3D-LUT is increased, it takes time to load the data to a memory. As a result, depending on a model or application of an image display device, there was a possibility that an adverse effect would be noticeable, for example, it would take time to perform switching of an output mode although such precision of color conversion was not necessary.